Corona treatment of polymer film surfaces is well known. "Corona," as used herein, refers to electrical discharges that occur at substantially atmospheric pressure, and is to be distinguished from sub-atmospheric and vacuum-pressure electrical discharges or processes, as well as from subatmospheric and atmospheric "glow" discharges as described in European Patent Publication No. 603784.
One purpose of corona treatment, or "corona-priming," of a polymer surface is to improve the interaction of the polymer surface with adhesives. Another purpose of corona treatment is to improve wettability of the surface. Corona priming of polymer films in air to increase interaction with adhesives and wettability of the surface is a well-known commercial process. Air corona priming is typically performed in the presence of ambient atmospheric gases (i.e., nitrogen and oxygen and trace gases) at atmospheric pressure. Corona processes are generally faster, cheaper, and more susceptible of application to in-line industrial processes than are sub-atmospheric and vacuum-pressure processes.